Assignment and Operations

Once you have declared a variable, you can store values in it.
This is called assignment.

To assign a value to a variable, follow this syntax:

variable_name:=expression;

Note that unlike other languages, whose assignment operator is
just an equals sign, Pascal uses a colon followed by an equals sign,
similarly to how it's done in most computer algebra systems.

The expression can either be a single value:

some_real := 385.385837;

or it can be an arithmetic sequence:

some_real := 37573.5 * 37593 + 385.8 / 367.1;

The arithmetic operators in Pascal are:

Operator

Operation

Operands

Result

+

Addition or unary positive

real or integer

real or integer

-

Subtraction or unary negative

real or integer

real or integer

*

Multiplication

real or integer

real or integer

/

Real division

real or integer

real

div

Integer division

integer

integer

mod

Modulus (remainder division)

integer

integer

div and mod only work on integers. / works on
both reals and integers but will always yield a real answer. The
other operations work on both reals and integers. When mixing integers and reals, the result will always be a real since data loss would result otherwise. This is why Pascal uses two different operations for division and integer division. 7 / 2 = 3.5 (real), but 7 div 2 = 3 (and 7 mod 2 = 1 since that's the remainder).

Each variable can only be assigned a value that is of the
same data type. Thus, you cannot assign a real value to
an integer variable. However, certain data types will convert to a higher data type. This is most often done when assigning integer values
to real variables. Suppose you had this variable
declaration section:

var
some_int : integer;
some_real : real;

When the following block of statements executes,

some_int := 375;
some_real := some_int;

some_real will have a value of 375.0.

Changing one data type to another is referred to as typecasting. Modern Pascal compilers support explicit typecasting in the manner of C, with a slightly different syntax. However, typecasting is usually used in low-level situations and in connection with object-oriented programming, and a beginning programming student will not need to use it. Here is information on typecasting from the GNU Pascal manual.

In Pascal, the minus sign can be used to make a value negative.
The plus sign can also be used to make a value positive, but is typically left out since values default to positive.

Do not attempt to use two operators side by side, like in:

some_real := 37.5 * -2;

This may make perfect sense to you, since you're trying to
multiply by negative-2. However, Pascal will be confused — it
won't know whether to multiply or subtract. You can avoid this by
using parentheses to clarify:

some_real := 37.5 * (-2);

The computer follows an order of operations similar to the one
that you follow when you do arithmetic. Multiplication and division
(* / div mod) come before addition and subtraction (+
-), and parentheses always take precedence. So, for example, the value of: 3.5*(2+3) will be 17.5.

Pascal cannot perform standard arithmetic operations on Booleans.
There is a special set of Boolean operations.
Also, you should not perform arithmetic operations on characters.